Question: What is $21\%$ of $300$ ?
Answer: Having $21\%$ of something means that you get $21$ out of every $100$ We can set up a proportion to find out what number is $21\%$ of $300$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We know the ${\text{percent}}$ is $21$ . Is $300$ the ${\text{part}}$ or the ${\text{whole}}$ The $300$ is the ${\text{whole}}$ . We are trying to find the ${\text{part}}$ that makes up $21\%$ of it: $ \dfrac{{21}}{100} = \dfrac{{\text{part}}}{{300}}$ If we multiply the denominator of the fraction on the left by $3$ , it will be the same denominator of the fraction on the right. To keep things equal, let's also multiply the numerator on the left by $3$ $ \dfrac{{21} \times 3}{100 \times 3} = \dfrac{{\text{part}}}{{300}}$ $ \dfrac{{63}}{300} = \dfrac{{\text{part}}}{{300}}$ $ {63} = {\text{part}}$ So $63$ is $21\%$ of $300$.